MT#55283 packet_encoded_tx: add a ts delay when transmitting DTMF event packets

when DTMF is being transmitted using codec_output_rtp, the scheduled
time to send the packet is calculated using the timestamp difference
from the last transmitted applied on top of the realtime time the
last packet was sent. However, the timestamp is only updated on the
first event packet so a delay needs to be passed in to codec_output_rtp
to ensure the subsequent packets are scheduled based on the event
duration of the event packets

Change-Id: I5a2f6cf67b5f570f6099d201592d9a6fc01d60a5
(cherry picked from commit 6aa10931ad)

daemon/codec.c

@@ -3923,6 +3923,7 @@ static void packet_encoded_tx(AVPacket *pkt, struct codec_ssrc_handler *ch, stru
 	// check special payloads
 
 	unsigned int repeats = 0;
+	unsigned long ts_delay = 0;
 	int payload_type = -1;
 	int dtmf_pt = ch->handler->dtmf_payload_type;
 	if (dtmf_pt == -1)
@@ -3938,6 +3939,12 @@ static void packet_encoded_tx(AVPacket *pkt, struct codec_ssrc_handler *ch, stru
 			ch->rtp_mark = 1; // DTMF start event
 		else if (is_dtmf == 3)
 			repeats = 2; // DTMF end event
+		// we need to pass a ts_delay to codec_output_rtp to ensure the calculated time
+		// to send the packet is offset by the event duration of the DTMF packets
+		// but we need to reduce it by one packet duration so that the delay is offset
+		// from the first event packet
+		struct telephone_event_payload *ev_pt = (void *) inout->s;
+		ts_delay = ntohs(ev_pt->duration) - (ch->handler->dest_pt.ptime * ch->handler->dest_pt.clock_rate / 1000);
 	}
 	else {
 		if (is_silence_event(inout, &ch->silence_events, pkt->pts, pkt->duration))
@@ -3956,7 +3963,7 @@ static void packet_encoded_tx(AVPacket *pkt, struct codec_ssrc_handler *ch, stru
 		codec_output_rtp(mp, &ch->csch, ch->handler, send_buf, inout->len, ch->csch.first_ts
 				+ fraction_divl(pkt->pts, cr_fact),
 				ch->rtp_mark ? 1 : 0, -1, 0,
-				payload_type, 0);
+				payload_type, ts_delay);
 		mp->ssrc_out->parent->seq_diff++;
 		ch->rtp_mark = 0;
 	} while (repeats--);